1. Field of the Invention
The present invention relates to a liquid crystal display device having a flexible printed circuit board, and more particularly to a liquid crystal display device having a flexible circuit board with a driving chip mounted thereon that connects a liquid crystal panel to a printed circuit board.
2. Description of the Related Art
A liquid crystal display device applies a voltage to a layer of liquid crystal to convert its molecular arrangement. The liquid crystal display device converts the changes of the optical properties of liquid crystal cells that transmits light according to the molecular arrangement, and uses the light modulation of the liquid crystal cells.
The liquid crystal display device is sorted into a TN (Twisted Nematic) type and a STN (Super-Twisted Nematic) type. The liquid crystal display device also can be sorted into an active matrix display type, which uses a switching device and a TN liquid crystal, and a passive matrix type, which uses an STN liquid crystal, according to the driving method. A TFT-LCD that drives an LCD by using a TFT has a relatively simple circuit, and it is widely used in computers.
The liquid crystal display device includes a liquid crystal panel to which electrical signals are applied to determine whether the light has been passed. The liquid crystal panel is a passive light device. So, a back light assembly for providing the liquid crystal display device with the light, is attached to the rear surface of the liquid crystal panel.
A source part that comprises a source driving IC for applying screen data to display the image, and a gate part that comprises a gate driving IC for applying gate signals for driving the gate device of a thin film transistor of the liquid crystal panel, are attached to the liquid crystal panel. The image signals that are applied from the outside are converted into data signals for driving the liquid crystal panel and gate signals for driving the thin film transistor. The data signals and the gate signals are applied to the transistor of the liquid crystal panel through the source part and the gate part. Therefore, the liquid crystal of the liquid crystal panel receives electrical signals, and the light from the back light assembly is regulated to display images.
The method of connecting the liquid crystal panel to the source and gate driving IC is sorted into a COG (Chip-On Glass) type and a TAB (Tape Automated Bonding) type. According to the COG type, a driving IC of a semiconductor package type is directly mounted to the gate and data areas of the liquid crystal panel, to transfer the electrical signals to the liquid crystal panel. The driving IC uses an anisotropic conductive film, and is bonded to the liquid crystal panel.
According to the TAB type, the liquid crystal panel is directly connected to the printed circuit board by using a tape carrier package to which the driving IC is mounted. One end of the tape carrier package is connected to the liquid crystal panel, and the other end of the tape carrier package is connected to the printed circuit board. Then, the input wire of the carrier package is connected to the output pad of the printed circuit board by soldering or using an anisotropic conductive film.
Examples of the liquid crystal panel modules that use the tape carrier package are disclosed in U.S. Pat. No. 5,572,346 issued to Sakamoto et al, and U.S. Pat. No. 6,061,246 issued to Oh et al. The conventional TFT liquid crystal modules mainly use the tape carrier package to mount the driving IC.
Recently, LCD modules of various structures have been developed to make it slim. In particular, considering that LCD modules are used in portable computers, the weight of the LCD module is important. If the tape carrier package is applied to the LCD modules, the flexibility is insufficient. Therefore, a flexible circuit board is used in an LCD module. A COF (Chip On Film) method is used to mount the driving IC on the flexible circuit board. According to the COF method, a chip is mounted onto the printed circuit board by using a TAB.
FIG. 1 is a top view showing a flexible circuit board onto which a chip is mounted by the COF method. FIG. 2 is a side cross-sectional view showing a liquid crystal module to which a flexible circuit board is mounted. Referring to FIGS. 1 and 2, a driving IC 20 for driving a liquid crystal panel is mounted at the center of the base film 10 of a tape-shape. The base film 10 comprises a printed circuit board engaging portion 12 for connecting a printed circuit board 30 and a liquid crystal panel engaging portion 14 for engaging with a liquid crystal panel 40. A solder resin layer 16 is formed between the printed circuit board engaging portion 12 and the liquid crystal panel engaging portion 14.
Input side conductive layer patterns 22 for transferring driving signals from the printed circuit board to the driving IC 20 are formed on the printed circuit board engaging portion 12. The solder resin layer 16 covers the input side conductive layer patterns 22 and is formed around the driving IC 20.
Output side conductive layer patterns 24 for applying the driving signals from the driving IC 20 to the liquid crystal panel are formed on the liquid crystal panel engaging portion 14. The solder resin layer 16 covers the output side conductive layer patterns 24 and is formed around the driving IC 20.
An align mark 26 is formed at the outmost patterns of the both sides of the output side conductive layer patterns 24 to easily engage the wires of the liquid crystal panel 14.
As shown in FIG. 2, a back light assembly 50 that provides the light is mounted in the liquid crystal display module. A display unit comprising the liquid crystal panel 40 is mounted onto the back light assembly. The input side of the liquid crystal panel 40 is connected to the output side conductive layer patterns 24 of the flexible circuit board.
The flexible circuit board wraps around the side wall of the mold frame 60, and is bent so as to adhere to the bottom surface of the mold frame 60. The input side conductive layer patterns 22 of the flexible circuit board are connected to the output side of the printed circuit board 30, and the printed circuit board 30 is adhered to the bottom of the mold frame 60. A polished inclined surface is formed at the end portion of the glass board of the liquid crystal panel 40.
The aforementioned conventional flexible circuit board is manufactured by the chip-on-film package method. By the chip-on-film package method, the reliability of the liquid crystal display device module of a thin film transistor and the manufacturing cost of the liquid crystal display device will be reduced.
However, since the flexible circuit board is too flexible, the border portion (A portion of FIGS. 1 and 2) of the solder resist 16 may contact the edge portion of the liquid crystal panel 40, which may cause disconnections.
The present invention has been made to solve the above-mentioned problems, and accordingly, it is the object of the present invention to provide a liquid crystal display device having a flexible circuit board that can prevent the output side conductive layer patterns from disconnection caused by bending and exterior stresses.
In order to achieve the aforementioned object of the present invention, the present invention provides a liquid crystal display device including a display unit having a liquid crystal display panel, and a flexible circuit board attached to the liquid crystal display panel, for applying driving signals to said liquid crystal display panel for driving the liquid crystal panel, a back light assembly that provides light to the display unit, a mold frame for receiving the liquid crystal display panel and the back light assembly, a chassis, being coupled to said mold frame, for fixing said liquid crystal display panel and said back light assembly to said mold frame. The flexible circuit board includes a flexible base film having a liquid crystal panel engaging portion. A driving IC is formed at the center of the base film and applies driving signals to driving devices of the liquid crystal panel. First conductive layer patterns are extended on the base film from the driving IC to the liquid crystal panel engaging portion, for electrically connecting the driving IC to the liquid crystal panel. A solder resin layer exposes the first conductive layer patterns formed on the liquid crystal panel engaging portion and covering the first conductive layer patterns of the periphery of the driving IC. A reinforcing means prevents the first conductive layer patterns from disconnecting due to the bending fatigue of the border portion of the liquid crystal panel engaging portion and the solder resin layer.
According to the present invention, the flexible circuit board includes a reinforcing member that can alleviate the inflection in the vicinity of the border surface of the solder resin layer. The reinforcing member can move the inflection point from the border of the solder resist layer, to the center of the solder resist layer. Therefore, the stresses on the solder resist layer are distributed, to effectively prevent the curvature changes caused by the inflection. It also prevents the cracks and disconnections of the output side conductive layer patterns formed in the vicinity of the border surface of the solder resin layer.